1. Field of the Invention
The present invention relates to a membrane switch, which is produced by interposing a spacer between flexible films having conductor circuits formed by the printing or the like. The present invention also relates to a dial operation member, which is equipped with such a membrane switch.
2. Description of the Related Art
Such a membrane switch is used as a switch including electrical circuits, which are formed by printing a conductive paste onto flexible substrates, such as polyester films or the like. The membrane switch is used as a lightweight, thin and flexible switch, and therefore is particularly useful for mass production. These significant features of the membrane switch allow it to be used in a wide application field, for instance, in a keyboard for a computer, a home electrical appliance, a portable communication device, such as a cellar phone, a component for an automobile, a musical instrument, a medical appliance and others.
FIG. 7 is a plan view of a conventional membrane switch. FIG. 8 is a plan view of a lower contact sheet in the conventional membrane switch. FIG. 9 is a plan view of an upper contact sheet in the conventional membrane switch. FIG. 10A is a sectional view of the conventional membrane switch in the non-conductive state, and FIG. 10B is a sectional view of the conventional membrane switch in the conductive state.
Such a conventional membrane switch 110 comprises a lower contact sheet 111, an upper contact sheet 112, a spacer 113, a connector 114 and others, as shown in FIGS. 7-10. The lower contact sheet 111 includes a conductor 111a and a projection portion 111b, as shown in FIG. 8. The conductor 111a includes several sets of paired contact areas 111c and 111d, each end of which is ramified in the form of an approximately U shape. The upper contact sheet 112 includes circular contact areas 112a, which are used to come into contact with the corresponding contact areas 111c and 111d in the conductive state, as shown in FIG. 9. In the spacer 113, there are through holes 113a, through which paired contact areas 111c and 111d on the side of the lower contact sheet 111 and corresponding contact areas 112a on the side of the upper contact sheet 112 come into contact with each other in the conductive state, as shown in FIG. 7. The projection portion 111b which is part of the lower contact sheet 111 including part of the conductor 111a is inserted into the connector 114.
In the following, the function of the conventional membrane switch will be described.
When trying to push a projection portion 109d to bend the upper contact sheet 112 in the lower direction by pushing a projection portion 109d, as shown in FIG. 10A, the contact area 112a is in contact with the paired contact areas 111c and 111d, as shown in FIG. 10B. Accordingly, the contact area 112a is directly connected to the paired contact areas 111c and 111d, so that the membrane switch 110 turns on in the conductive state (the ON state).
In the conventional membrane switch 110, there is a problem in which a decrease in the press force acting to the upper contact sheet 112 occasionally causes the contact area 112a to come in contact with only one of the paired contact areas 111c and 111d, so that the membrane switch 110 does not turn on in the conductive state. Furthermore, in order to securely connect the contact area 112a with both the contact areas 111c and 111d in the conventional membrane switch 110, it is necessary that the projection portion 109d made of a resilient material, such as gum or the like, presses against the upper contact sheet 112 with a press force greater than a predetermined force. This also provides an increase in the production cost, since the number of the parts constituting the membrane switch 110 is inevitably increased.
Accordingly, it is an object of the present invention to provide a membrane switch capable of turning on even with a very small weight.
It is another object of the present invention to provide a dial operation member, which is equipped with such a membrane switch.
In accordance with a first aspect of the invention, a membrane switch comprises,
(a) a first base element made of an electrical insulation elastic material, the first base element having a first conductor including at least one press contact area and at least one permanent contact area on a surface of the first base element;
(b) a second base element made of an electrical insulation material, the second base element having a second conductor and a third conductor on a surface facing the surface of the first base element,
the second conductor including at least one press contact area in accordance with the arrangement of the at least one press contact area in the first conductor, and
the third conductor including at least one permanent contact area in accordance with the arrangement of the at least one permanent contact area in the first conductor,
the second base element further having a connector section for connecting the second and third conductors to an external circuit; and
(c) a spacer made of an electrical insulation material, the spacer being interposed between the first base element and the second element, the spacer having through holes at positions corresponding to those both in the at least one press contact area and the at least one permanent contact area of the first and second base elements.
In accordance with a second aspect of the invention, a membrane switch comprises,
(a) a first base element made of an electrical insulation elastic material, the first base element having a first conductor including at least one press contact area, a second conductor including at least one permanent contact area and a connector section for connecting the first and second conductors to an external circuit on a surface of the first base element;
(b) a second base element made of an electrical insulation material, the second base element having a third conductor on the surface facing the surface of the first base element, the third conductor including at least one press contact area in accordance with the arrangement of the at least one press contact area disposed in the first conductor and the at least one permanent contact area in accordance with the arrangement of the at least one permanent contact area disposed in the first conductor; and
(c) a spacer made of an electrical insulation material interposed between the first base element and the second base element, the spacer having through holes in accordance with the arrangement of the at least one press contact area and the at least one permanent contact area.
In accordance with a third aspect of the invention, a dial operation member comprises,
(a) a shaft;
(b) a bearing through which the shaft passes;
(c) a dial body fixed to the shaft and rotatably supported around the center axis of the shaft;
(d) a press member for switch disposed so at to face the dial body for switching, the press member having at least one press projection portion for switching; and
(e) one of the above mentioned membrane switches, wherein at least one press portion for switching is disposed so as to face the at least press projection for switching in the press member for switch.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiment with reference to the accompanying drawings.